Optical recording medium with grooves, optical recording medium master with grooves, apparatus for manufacturing optical recording medium master with grooves, and optical recording/reproducing apparatus

ABSTRACT

The stable reproduction of wobble signal without generating beats despite of an improvement in recording density by narrowing a track pitch is realized. Data by magnetooptical recording is recorded on wobbling grooves and lands between adjacent wobbling grooves. The wobbling grooves are provided to wobble both sides of the grooves in different amplitudes. Further, both the sides wobbled in different amplitudes are wobbled in phase in the track direction. These different amplitudes of both sides are preferably set to 3.3 to 40%.

TECHNICAL FIELD

The present invention relates to an optical recording medium, an opticalrecording medium master, an apparatus for manufacturing opticalrecording medium master and an optical recording/reproducing apparatus.

BACKGROUND ART

An optical recording medium allows recording various signalizedinformation to optically reproduce. There are various kinds of recodingtype such as: read-only type optical discs in which embossed pitscorresponding to data are preformed on a disc substrate, such as compactdiscs and laser discs; magneto optical discs on/from which data isrecorded and reproduced utilizing a magnetooptical effect, such as MiniDiscs (MD); and phase-change optical discs on/from which information(data) is recorded and reproduced utilizing phase change of a recordinglayer, such as Digital Versatile Discs (DVD).

In the optical recording medium capable of rewriting information, suchas magneto optical discs and phase-change optical discs, contiguousgrooves instead of discrete pits are formed along a recording track. Thegrooves are provided for mainly controlling tracking servo, so-calledguide grooves. The interspaces between the grooves are called landsbecause they protrude in the position close to the surface of thegrooves than the bottom thereof.

The optical recording medium formed with the grooves generally performsa tracking servo control by using a push-pull signal. In order to obtainthe push-pull signal, a light beam is irradiated toward the opticalrecording medium and the light reflected by the optical recording mediumis detected with two photodetectors placed symmetrical to the center ofthe track, thereby the push-pull signal can be obtained based on adifference in the outputs from two photodetectors.

The applicant has proposed a method of forming wobbling wide grooves,which is a data recording area of MD, by superimposing the signals of22.05 kHz and 5 MHz in Japanese Patent No. 2960018. In this method, FMmodulation signal of 22.05 kHz is for recording wobble information ofaddress, whereas the signal of 5 MHz is for widening the groove width inaccordance with the amplitude. With this method, the wobbling widegrooves are formed to wobble both sides of the grooves. The datarecording area becomes wide grooves by forming the wobbling wide groovesin the optical recording medium. This achieves the stable reproductionof wobble signal of ADIP and the stable recording/reproducing of MOsignal.

Japanese Patent No. 2854187 proposes the technique that one side of thegrooves is wobbled and the other side is not wobbled but in straight(circular arc). According to the technique, address information can bestored in the wobbles of the grooves.

A high recording density and the stable reproduction of the wobblesignal are required in the optical recording medium formed with thewobbling grooves.

However, in the optical recording medium in which one side of thegrooves are wobbled as disclosed in Japanese Patent No. 2854187, theother side of the grooves which is not wobbled is not used for storingthe address information. As a result, the wobble signal amount is abouthalf of the optical recording medium in which both sides of the groovesare wobbled, thereby resulting in a problem of the difficulty of thestable reproduction of the wobble signal.

In addition, the stable reproduction of the wobble signal is desired byincreasing the wobble signal amount. However, in order to form thegrooves in which both sides thereof are wobbled and to improve therecording density, it is necessary to narrow a track pitch. The narrowtrack pitch generates beats in the wobble signal between the neighboringwobbles specifically in case of an out-of-phase wobble. This results inthe problem of the difficulty of the stable reproduction of the wobblesignal.

The present invention has been achieved in view of the above problems.It is an object of the invention to provide an optical recording mediumcapable of stably reproducing the wobble signal without generating beatseven if the track pitch is narrowed to improve the recording density.Further, the present invention provides an optical recording/reproducingapparatus used for recording/reproducing on/from the optical recordingmedium, an optical recording medium master used for replicating theoptical recording medium and an apparatus for manufacturing opticalrecording medium master.

DISCLOSURE OF THE INVENTION

The optical recording medium and the optical recording medium master ofthe invention have grooves on a surface of a substrate to constitute agroove track and are able to read information along a track of thegrooves. The grooves are wobbling grooves provided to wobble both sidesof the grooves in different amplitudes.

Another optical recording medium and the optical recording medium masterof the invention have grooves on a surface of a substrate to constitutea groove track and are able to read information along a track of thegrooves. The grooves are wobbling grooves provided to wobble both sidesof the grooves in phase in different amplitudes.

A manufacturing apparatus for the optical recording medium master of theinvention patterns grooves forming a track on a surface of a master,wherein a light beam for exposure or a laser beam is relatively traveledon a surface of a master of an optical recording medium with waving at acertain period in a direction intersect with a traveling based on acontrol signal superimposing a low-frequency signal and a high-frequencysignal, and a latent image is formed to become wobbling grooves wobblesboth sides of the grooves in phase in different amplitudes.

An optical recording/reproducing apparatus of the invention recordsand/or reproduces information on/from an optical recording medium havingwobbling grooves provided to wobble both sides of grooves in differentamplitudes and recording information both on the wobbling grooves and onlands, comprises: a means for traveling a light spot on the wobblinggrooves; and a means for detecting a wobble signal by traveling thelight spot on the wobbling grooves.

Another optical recording/reproducing apparatus of the invention recordsand/or reproduces information on/from an optical recording medium havingwobbling grooves provided to wobble both sides of grooves in differentamplitudes and recording information either on the wobbling grooves oron lands, comprises: a means for traveling a light spot on the wobblinggrooves; and a means for detecting a wobble signal by traveling thelight spot on the wobbling grooves.

In the optical recording medium, the master for the optical recordingmedium, the manufacturing apparatus of the master for the opticalrecording medium and the optical recording/reproducing apparatus of theinvention, the grooves are wobbling grooves provided to wobble bothsides of the grooves thereof in different amplitudes. Further, bothsides wobble in different amplitudes are wobbled in phase in the trackdirection. These different amplitudes of both sides are preferably setto 3.3 to 40%.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic structure of a magneto optical disc accordingto an embodiment of the invention.

FIG. 2 is an enlarged view showing a recoding area formed on a surfaceof the magneto optical disc shown in FIG. 1.

FIG. 3 shows a schematic structure of a laser cutting apparatus forproducing a master for the magneto optical disc of an embodiment of theinvention.

FIG. 4 schematically shows an exposure method for forming the wobbleshaving different amplitudes on both sides of wobbling grooves in phase.

FIG. 5 shows a schematic structure of the wobbling grooves obtained bythe exposure method shown in FIG. 4.

FIG. 6 shows the results of the measurement of jitter as a typical valueof recoding/reproducing characteristic of the evaluation magneto opticaldisc.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be described inmore detail below referring to the accompanying drawings.

[Magneto Optical Disc]

FIG. 1 shows a schematic structure of a magneto optical disc of anembodiment of the invention. The magneto optical disc is a disc shapedoptical recording medium recoding/reproducing data by the magnetoopticaleffect compliant with MD3 format standards.

A recoding area 3 recoding magnetooptically, a protective layer 4covering the whole surface of the recording area for protection arelaminated in this order on a disc substrate 2 made of glass,polymethylmethacrylate (PMMA) or polycarbonate (PC). Although not shownin FIG. 1, the recoding area 3 comprises, for example, a firstdielectric film made of SiN (silicon nitride), a perpendicular recordingfilm made of a TeFeCo alloy, a second dielectric film made of SiN, areflective film made of an Al alloy or the like in this order. Theprotective layer 4 is formed on the recording area 3 by spin coating anultraviolet curing resin. The materials for the recording area 3 and theprotective layer 4 are not limited to the above. The materials capableof effective magnetooptical recording can be used for forming therecording area 3. Any kinds of materials which can effectively protectthe recording area 3 can be used for forming the protective layer 4.

FIG. 2 is an enlarged view of the recording area formed on a surface ofthe magneto optical disc. The recording area can write magnetoopticalrecoding data on wobbling grooves 71 and lands 72 formed between theadjacent wobbling grooves 71.

The wobbling grooves 71 have an amplitude of ±15 nm on one side (theright side in FIG. 2) and an amplitude any of ±0.5 nm, ±1.5 nm, ±3.0 nmor ±6.0 nm on the other side, for instance, and wobble at substantiallyconstant period in phase in the longitudinal direction of the wobblinggrooves 71. The track pitch is 1.2 μm and the widths of the substantialwriting area of the wobbling grooves 71 and the lands 72 are about 0.60μm. The track pitch is the distance between the centers of the wobblesof the neighboring tracks.

The magneto optical disc is a Land and Groove Format in which theaverage widths of the wobbling grooves 71 and the lands 72 areapproximately equal. Therefore, enough level of push-pull signal can beobtained to perform the tracking servo control. The push-pull signal canbe obtained based on a difference between output SA and output SB(SA−SB). The outputs SA and SB can be determined by detecting thereflected light obtained by irradiating a light beam toward the magnetooptical disc with two photodetectors A and B (not shown) placedsymmetrical to the center of the track. The amount of reflective lightcan be determined by the sum of the output SA from the photodetector Aand the output SB from the photodetector B (SA+SB). The detectedinformation of the amount of reflective light (the sum signal of SA+SB)is used for detecting the number of straddle of the tracks when a lightbeam spot travels across the wobbling grooves 71 in the width directionthereof. This is generally called a cross track signal.

As described, the wobbling grooves 71 are provided to wobble both sidesin phase in different amplitudes and the address information is stored(added or included) in the wobbling grooves 71. As a result, compared tothe case where the wobbling grooves 71 are provided to wobble one sidethereof, the wobble signal amount is increased by 3.3% to 40%. Moreover,the wobbles on both sides are in phase and the amplitude of one side ofthe wobbling grooves 71 is ±15 nm and the other side is ±6.0 nm at themaximum, so when both sides of the wobbling grooves 71 are wobbled,sufficient signal amount can be obtained. In addition, the beatsgenerated in the wobble signal during the recording/reproducinginformation can be reduced or eliminated, thereby the stablerecording/reproducing is achieved.

Furthermore, enough push-pull signal for the tracking servo control canbe obtained from both wobbles of the wobbling grooves 71 havingdifferent amplitudes. This enables to perform the sure tracking stably.

[Laser Cutting Apparatus and Fabrication of Master using the Same]

A master (a master for manufacturing the optical recording medium) isused for manufacturing the magneto optical disc by, for example, aninjection molding apparatus. The master is manufactured by the lasercutting apparatus shown in FIG. 3.

The laser cutting apparatus exposes a photoresist 12 applied on a glasssubstrate 11 and forms a latent image of the planar pattern such as thewobbling grooves 71.

In the manufacturing process of the master, first, the glass substrate11 applied with the photoresist 12 thereon is set on a turntable 17 of arotative driving device (not shown). In the exposure process of thephotoresist 12, the glass substrate 11 with the photoresist 12 isrotative driven by the turntable 17 as indicated by an arrow M in thefigure. Moving optical table 18 irradiates a laser beam 30 on thephotoresist 12 while moving in parallel. Thereby, a desired pattern isexposed on the whole photoresist 12 on the glass substrate 11.

Specifically, the relative rotational speed (linear speed) of the masterby the turntable 17 to the laser beam 30 during the exposure is 0.91 m/sand the moving optical table 18 moves in parallel by the track pitch of1.20 μm per rotation, for instance. The rotational speed and theabsolute value of the track pitch are not limited to this.

More specifically, as a laser light source system, a laser light source13 emitting laser light, an EOM (Electro Optical Modulator) 14 foradjusting the intensity of the laser light emitted from the laser lightsource 13, a BS (Beam Splitter) 16 for dividing the laser light emittedform the EOM 14 into transmitted light and reflective light, an analyzer15 placed on the light axis of the laser light emitted from the EOM 14,a PD (Photo Detector) 19 receiving the laser light pass through theanalyzer 15 and APC (Auto Power Controller) 20 for feedback controllingof the intensity of the laser light emitted from the EOM 14 withapplying the signal electric field to the EOM 14 are comprised.

Kr (krypton) laser having a wavelength λ of 351 nm or the like, whichcan emit short wavelength laser light, is desirable as the laser lightsource 13, although this is not limited.

The laser light emitted form the laser light source 13 are adjusted to apredetermined light intensity by EOM 14 which is controlled and drivenby the APC 20 and enters the analyzer 15. Here, the analyzer 15 is Spolarized light, so the laser light pass through the analyzer 15 becomesS polarized light.

The laser light which is emitted from the laser light source 13 andtravels straight via the EOM 14, the BS 16 and the analyzer 15 isreceived by the PD 19. The PD 19 detects the light intensity and sendsthe signal storing information of the light intensity to the APC 20.Upon receiving the signal, the APC 20 adjust the signal electric fieldby entering the control signal to the EOM 14 to uniform the laser lightintensity received by the PD 19. The automatic control of the lightamount of the laser light source system keeps the constant intensity ofthe laser light emitted from the EOM 14.

On the other hand, the laser light reflected by the BS 16 travels as aparallel beam is reflected by a mirror 21 to change the direction andconducted to an AOD (Acoustic Optical Deflector) 48 in the movingoptical table 18.

The moving optical table 18 comprises the AOD 48, a drive circuit 50, areflective mirror 22, a beam magnifying lens 55 and an objective lens54. The AOD 48 comprises an acoustic optical element 46 and wedge prisms47 and 49 placed front and the back of the light axis of the acousticoptical device 46. These are placed to make the lattice plane of theacoustic optical element 46 and the wedge prisms 47 and 49 satisfy theBragg's condition of diffraction and not to change the horizontal heightof the light axis. As the acoustic optical element 46, tellurium oxide(TeO₂) can be preferably used. The AOD 48 is controlled based on the DCsignal from the drive circuit 50 to modulate the laser light intensity.

A voltage frequency controller 51 provides a high-frequency signal tothe drive circuit 50. The control signal is externally provided to thevoltage frequency controller 51. The control signal has a waveform inwhich a sinusoidal wave signal having a frequency of 5 MHz issuperimposed on a sinusoidal wave signal having a frequency of 84.672kHz. The sinusoidal wave of a frequency of 84.672 kHz wobbles the planerpattern of the wobbling grooves 71, while the amplitude of thesinusoidal wave of a frequency of 5 MHz widen the groove width of theplaner pattern of the wobbling grooves 71.

The control signal controls the AOD 48 to change the Bragg diffractionangle of the acoustic optical element 46 in the AOD 48. This generatesthe wobbles storing the address information in the laser beam 30. Atthis time, the laser beam 30 is controlled to have a constant spot andconverged on the master.

More specifically, in order to widen the width of the wobbling grooves71, a spatial frequency of polarization frequency is adjusted and mademultiple exposures to become smaller amplitude than a radius of laserbeam 30 irradiating on the master. In other words, assuming the linearspeed of the laser beam 30 relatively traveling on the master is v, thepolarization frequency is f, a diameter of the laser beam is D, v/f≦D.For example, when v=0.91 m/s, D=0.35 μm and f is 2.6 MHz or more (f≧2.6MHz), the width of the wobbling grooves 71 can be widened.

FIG. 4 schematically shows an exposure method for forming the wobbleshaving different amplitudes on both sides of the wobbling grooves 71 inphase, as described above. FIG. 5 schematically shows the wobblinggrooves 71.

A D/A converter provided with an external reference voltage and capableof obtaining the output in proportion to the external voltage isprepared. The clockpulse double the frequency of 5 MHz is applied andthe level data equivalent to 100% output and 50% output, respectively isrepeatedly applied. The external reference voltage is voltage in whichoffset equivalent to 50% of reference voltage Vs is applied to thelow-frequency wobble signal. For example, the external reference voltageVo is Vo=Vs×0.5 (direct current)+low-frequency wobble signal (10% pp).If necessary, DC offset is applied to the output signal to eliminate thedirect current component.

The envelope of the positive side of the high-frequency signal waveform(this defines the right side in FIG. 4) is 10% pp, whereas the envelopeof the negative side (this defines the left side in FIG. 4) is 5% pp.This enable to obtain the control signal whose ratio of the amplitude ofthe envelope waveform of the positive side and the negative side of thehigh-frequency signal waveform is 2:1. However, the ratio of theamplitude of the envelope waveform is not limited to the above.

Variation of the ratio of the level data applied to the D/A convertercan vary the modulation degree of the envelope waveform. Making one ofthe level data a negative voltage reverses the phase of the negativeside and the positive side, thereby enabling the wobbles on both sidesof the wobbling grooves 71 become mutually the opposite phase. It ispossible to vary the amplitude of the high-frequency signal by changingthe direct current offset voltage applied as the external referencevoltage.

The control signal generated as described above is applied to the drivecircuit 50 as a signal corresponding to the exposure pattern from thevoltage frequency controller 51 during the exposure of the photoresist12. Based on the signal, the drive circuit 50 drives the AOD 48, opticalpolarization is performed on the laser beam 30 for exposing thephotoresist 12, and the planar pattern of the wobbling grooves 71wobbling both sides thereof in phase in different amplitudes can beexposed on the photoresist 12 of the master.

Specifically, when storing the address information by wobbling thewobbling grooves 71 with a frequency of 84.672 kHz, the low-frequencysignal and the high-frequency signal, which are FM modulated into 84.672kHz and 5 MHz, respectively by use of a high-frequency signal having acenter frequency of 224 MHz, are superimposed to generate the controlsignal. The obtained control signal is applied to the drive circuit 50from the voltage frequency controller 51. Based on the applied signal,the drive circuit 50 changes the Bragg angle of the acoustic opticaldevice 46 of the AOD 48, the polarization is performed acousticoptically on the laser beam 30, and the pattern wobbled both sides inphase in different amplitudes can be exposed.

The laser beam 30 applied the acoustic optical polarization by the AOD48 is adjusted to a predetermined beam spot diameter by the beammagnifying lens 55, reflected by the mirror 22 and conducted to theobjective lens 54. After that, the laser beam 30 is irradiated on thephotoresist 12 on the master by the objective lens 54 while waving inthe direction intersect with the groove direction of the wobblinggrooves 71 as shown in FIG. 4. Thereby, the latent image including thepattern which wobbles both sides of a wobbling grooves 71 in phase indifferent amplitudes is formed on the photoresist 12. The planer patternof the wobbling grooves 71 wobbles both sides thereof in differentamplitudes is exposed by periodically waving one beam spot withdifferent amplitudes based on the control signal superimposing thelow-frequency signal and the high-frequency signal. As a result, nophase lag (or synchronous lag) is generated on both sides of the wobblesunlike the case where the wobbles on both sides of a wobbling groove 71is exposed by using the different beam spots. This ensures the exposureof the wobbles on both sides in phase.

It is preferable for the objective lens 54 to have a larger NA(numerical aperture) in order to form the smaller loop pattern with ahigh accuracy. Specifically, the objective lens 54 with an NA of 0.9 ormore is preferable.

After forming the latent image on the photoresist 12 on the master, themaster is developed by dissolving exposed part of the photoresist 12. Inparticular, an undeveloped master is set on the turntable of processor,which is not shown. Then it is rotated with the turntable and developeris dropped on the surface of the master to develop the photoresist 12.

Subsequently, a conductive film of nickel (Ni) thin film is formed onthe uneven pattern of the photoresist 12 on the master by electrolessplating machine (not shown). The master formed with the conductive filmis set on the gilding machine, which is not shown, and a nickel-platinglayer with a thickness of about 300±5 μm is formed on the conductivefilm by electroplating, for example.

Then, the nickel-plating layer is separated from the master by cutter,squeegee for separation or the like and the photoresist 12 remaining onthe surface in which the nickel-plating layer was formed is cleanedusing acetone or the like to obtain stamper incorporated in a mold foran injection molding.

Using the stamper, the minute concavity and convexity in the wobblinggrooves 71 and so on formed on the surface of the master are transferredon a surface of a base plate 1 by photopolymerization process (theso-called 2P process). For example, first, photopolymer is evenlyapplied on the surface formed with the concavity and convexity of themaster to form a photopolymer layer 7. On the photopolymer layer 7, thebase plate 1 of glass with a thickness of 1.2 mm and a refractive indexof 1.52 or less is adhered while avoiding the mix of air bubble, dustand the like. Then, the photopolymer layer 7 is hardened by ultravioletirradiation, and is separated form the master together with the baseplate 1. Thereby, the disc substrate 2 on which the minute concavity andconvexity of the surface of the master is transferred on thephotopolymer layer 7 can be obtained.

A first dielectric film made of silicon nitride (Si₃N₄), a DWDD (DomainWall Displacement Detection) film made of a TbFeCo alloy, a DyFeCoalloy, a GdFe alloy or the like, a second dielectric film made ofsilicon nitride and a reflective film made of an aluminum alloy (Al—Ti)are deposited in this order on the recording surface of the discsubstrate 2 as shown in FIG. 1 as the recording area 3. After that, onthe reflective film, 2P resin is smoothly applied to cover almost wholesurface (top surface) of the substrate by, for example, spin coat methodand hardened by irradiating UV lamp to form the protective layer 4.Thereby, the magneto optical disc of the embodiment is achieved.

In the embodiment, as a method that the concavity and convexity patternof the wobbling grooves 71 or the like formed on the master is preciselytransferred on the disc substrate 2, a method using photopolymer isdescribed. However, in case of mass production with high efficiency ofthe disc substrate 2, a transparent resin such as polymethylmethacrylateand polycarbonate may be formed with injection molding to manufacturethe disc substrate 2 formed with the concavity and convexity pattern ofthe wobbling grooves 71 thereon.

The materials for forming the base plate 1, the recording area 3, theprotective layer 4 or the like of the magneto optical disc is notlimited to the materials described above, so other materials can beused.

EXAMPLE

A plural evaluation magneto optical discs having the various amplitudeof the wobbling grooves or the like were fabricated by the method usingthe master as described and the recording/reproducing capability wereevaluated on each evaluation magneto optical disc.

In order to conduct an evaluation experiment of the evaluation magnetooptical discs, first, the masters were fabricated. In the manufacturingprocess of the masters, the power of the laser beam 30 for exposure wasvaried to check the change in the groove width per power. Specifically,the power of the laser beam 30 was set to 0.9, 1.1 and 1.45 and thewidths of the wobbling grooves 71 of the masters were measured on eachcase by use of an electron microscope. The groove widths were 562 nm,622 nm and 682 nm in accordance with the above powers, respectively.Each amplitudes of one side of the disc was ±15 nm, and the other sideswere set to have different amplitudes of ±0.5 nm, ±1.5 nm, ±3.0 nm and±6.0 nm, respectively.

Using the masters fabricated as described above, the disc substrate 2was formed by the above-described photopolymer process and the recordingarea 3 and the protective layer 4 were formed on the surface thereon tofabricate the evaluation magneto optical discs.

The reproducing characteristics of the wobble signal and therecording/reproducing characteristics of the magnetooptical recordinglayer were measured on each evaluation magneto optical discs fabricatedas described above. The optical pickup in which a wavelength λ of laserlight is 650 nm and NA of the objective lens 54 is 0.52 was used for themeasurement and the reading and reproducing were performed on thewobbling grooves 71 and the lands 72 with 1–7 modulation.

The results showed the stable reproduction of the wobble address signalin all evaluation magneto optical discs.

Further, the jitter as a typical value (parameter) of therecording/reproducing characteristics in the magnetooptical recordinglayer was measured on the evaluation magneto optical disc in which theamplitude of one side of the wobbling grooves 71 was ±15 nm and theother side thereof was ±6.0 nm. The results are shown in FIG. 6. Namely,when the groove width was 562 nm, the jitter in the lands 72 was 10.5%and the jitter in the wobbling grooves 71 was 9.5%. Further, when thegroove width was 622 nm, the jitter in the lands 72 was 9.5% and thejitter in the wobbling grooves 71 was 8.5%. Furthermore, when the groovewidth was 682 nm, the jitter in the lands 72 was 10.0% and the jitter inthe wobbling grooves 71 was 8.5%. The recording/reproducingcharacteristics of all evaluation magneto optical discs were stableenough. In the case where the amplitude of the other side of thewobbling grooves 71 is less than ±6.0 nm, it is assumed that furtherstable recording/reproducing characteristics can be obtainedtheoretically. In fact, it was confirmed that the recording/reproducingcharacteristics measuring the jitter as a typical value was more stable.

In all evaluation magneto optical discs in which the amplitude of oneside of the wobbling grooves 71 was ±15 nm and the other side thereofwere within the range between 0.5 nm at the minimum and 6.0 nm at themaximum, the stable recording/reproducing characteristics was obtained.It revealed that setting the ratio of amplitude of one side of thewobbling grooves 71 having a smaller amplitude to the other side thereofhaving a larger amplitude within the range from 3.3% to 40% enabled toobtain the stable recording/reproducing characteristics.

The invention is wildly applicable to an optical recording mediumcapable of forming different amplitudes of the wobble in both sides ofthe grooves, a master and a manufacturing method thereof and an opticalrecording apparatus.

The invention is also applicable to a rewritable optical recordingmedium capable of rewriting data more than once, a recordable opticalrecording medium capable of recording and incapable of deleting and aread-only optical recording medium in which data incapable of rewritingis prerecorded.

In addition, the invention is applicable to any recording type of datasuch as a read-only type, a magnetooptical type recording/reproducingdata utilizing the magnetooptical effect and a phase-change typerecoding/reproducing data using the phase change of the recording layer.

Furthermore, the invention is applicable to the optical recording mediumin which the data recording area is formed only in the lands, only inthe grooves, or both the lands and the grooves as well as the opticalrecording medium in which the embossed pits and the wobbling grooves areformed together in one disc.

As described, the optical recording medium, the optical recording mediummaster, manufacturing apparatus of the optical recording medium masterand the optical recording/reproducing apparatus of the invention, thegrooves are the wobbling grooves provided to wobble both sides of thegrooves in different amplitudes. Further, both sides of the grooves arewobbled in phase in the track direction. As a result, even if the trackpitch is narrowed to improve the recording density, the effect such thatthe stable wobble signal is reproduced without generating beats areachieved.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

1. An optical recording medium in which grooves are formed on a surfaceof a substrate to constitute a groove track and information can be readalong a track of the grooves, wherein the grooves are wobbling groovesprovided to wobble both sides of the grooves in different amplitudes,and the wobbling grooves have a ratio of amplitude of one side of thewobbling grooves having a smaller amplitude to the other side thereofhaving a larger amplitude within the range from 3.3% to 40%.
 2. Anoptical recording medium according to claim 1, wherein information canbe recorded on grooves of the wobbling grooves and on lands between theadjacent wobbling grooves.
 3. An optical recording medium in whichgrooves are formed on a surface of a substrate to constitute a groovetrack and information can be read along a track of the grooves, whereinthe grooves are wobbling grooves provided to wobble both sides of thegrooves in phase in different amplitudes, and the wobbling grooves havea ratio of amplitude of one side of the wobbling grooves having asmaller amplitude to the other side thereof having a larger amplitudewithin the range from 3.3% to 40%.
 4. An optical recording mediumaccording to claim 3, wherein information can be recorded on grooves ofthe wobbling grooves and on lands between the adjacent wobbling grooves.5. An optical recording medium master used for manufacturing an opticalrecording medium in which grooves are formed on a surface of a substrateto constitute a groove track and information can be read along a trackof the grooves, wherein the grooves are wobbling grooves provided towobble both sides of the grooves in different amplitudes, and thewobbling grooves have a ratio of amplitude of one side of the wobblinggrooves having a smaller amplitude to the other side thereof having alarger amplitude within the range from 3.3% to 40%.
 6. An opticalrecording medium master according to claim 5, wherein an opticalrecording medium in which information can be recorded on grooves of thewobbling grooves and on lands between the adjacent wobbling grooves ismanufactured.
 7. An optical recording medium master in which grooves areformed on a surface of a substrate to constitute a groove track andinformation can be read along a track of the grooves, wherein thegrooves are wobbling grooves provided to wobble both sides of thegrooves in phase in different amplitudes, and the wobbling grooves havea ratio of amplitude of one side of the wobbling grooves having asmaller amplitude to the other side thereof having a larger amplitudewithin the range from 3.3% to 40%.
 8. An optical recording medium masteraccording to claim 7, wherein an optical recording medium in whichinformation can be recorded on grooves of the wobbling grooves and onlands between the adjacent wobbling grooves is manufactured.
 9. Amanufacturing apparatus for an optical recording medium masterpatterning grooves forming a track on a surface of a master, wherein alight beam for exposure or a laser beam is relatively traveled on asurface of a master of an optical recording medium with waving at acertain period in a direction intersect with a traveling based on acontrol signal superimposing a low-frequency signal and a high-frequencysignal, and a latent image is formed to become wobbling grooves wobblesboth sides of the grooves in phase in different amplitudes, wherein thewobbling grooves have a ratio of amplitude of one side of the wobblinggrooves having a smaller amplitude to the other side thereof having alarger amplitude within the range from 3.3% to 40%.
 10. A manufacturingapparatus for an optical recording medium master according to claim 9,wherein wobbles on both the sides are kept in phase and amplitudes ofthe wobbles on both the sides are independently controlled.
 11. Anoptical recording/reproducing apparatus recording/reproducinginformation on/from an optical recording medium having wobbling groovesprovided to wobble both sides of grooves in different amplitudes andrecording information both on the wobbling grooves and on lands,comprising: a means for traveling a light spot on the wobbling grooves;and a means for detecting a wobble signal by traveling the light spot onthe wobbling grooves, wherein the wobbling grooves have a ratio ofamplitude of one side of the wobbling grooves having a smaller amplitudeto the other side thereof having a larger amplitude within the rangefrom 3.3% to 40%.
 12. An optical recording/reproducing apparatusrecording/reproducing information on/from an optical recording mediumhaving wobbling grooves provided to wobble both sides of grooves indifferent amplitudes and recording information either on the wobblinggrooves or on lands, comprising: a means for traveling a light spot onthe wobbling grooves; and a means for detecting a wobble signal bytraveling the light spot on the wobbling grooves, wherein the wobblinggrooves have a ratio of amplitude of one side of the wobbling grooveshaving a smaller amplitude to the other side thereof having a largeramplitude within the range from 3.3% to 40%.